This application claims the benefit of a Japanese Patent Application No. 2001-214060 filed Jul. 13, 2001, in the Japanese Patent Office, the disclosure of which is hereby incorporated by reference.
1. Field of the Invention
The present invention generally relates to smoothing methods, smoothing circuits, image forming apparatuses and display units, and more particularly to a smoothing method and a smoothing circuit for obtaining high-quality image data by eliminating jaggy or the like from the image data, and to an image forming apparatus and a display unit which employ such a smoothing method.
Image data generated by a computer or the like are output by an image output apparatus such as a printer and a display unit. Recently, there are increased demands to output clearer and sharper images, and the resolution of the image output apparatuses such as printers and display units have improved considerably.
In order to more effectively utilize the image output apparatus having such an improved resolution, a smoothing process is carried out. The smoothing process is an image quality improving process for making jagged pixels (dots) less inconspicuous, that is, for making the jaggy less conspicuous, in a case where the image is made up of characters or lines. This smoothing process becomes necessary when outputting the image data having a relatively low resolution as image data having a high resolution. For example, the image data having the relatively low resolution are developed into an image in the computer or transmitted by a communication means such as a facsimile machine.
2. Description of the Related Art
FIG. 1 is a system block diagram for explaining an example of a conventional smoothing circuit. The smoothing circuit shown in FIG. 1 generally includes an input image buffer 1, a template matching circuit 2, and a flip-flop (FF) 3. Such a smoothing circuit is proposed in a Japanese Laid-Open Patent Application No. 2000-358149, for example.
As shown in FIG. 1, a rectangular region having a predetermined size is extracted as an extracted window pattern 5 from a binary input image data which is input to an input image buffer 1. An image input clock which is used to synchronize the operation timings is input to the input image buffer 1 and the flip-flop which will be described later. The template matching circuit 2 collates the window pattern 5 with a predetermined collating template group 6 which is stored within the template matching circuit 2. Each collating template of the collating template group 6 has a pattern for extracting features of contour portions, and includes corrected dot data in correspondence with the features of the respective contour portions. If there exists a collating template which matches the input window pattern, the template matching circuit 2 outputs the corrected dot data of the matching collating template via the flip-flop 3. The corrected dot data which is output has a dot pattern for making a dot correction with respect to a target pixel 7 which is located at the center of the extracted rectangular region, and the image quality is improved thereby.
FIGS. 2A and 2B are diagrams for explaining the smoothing process which is carried out by the smoothing circuit shown in FIG. 1. By carrying out the smoothing process by the smoothing circuit, a stepped contour having a low resolution as shown in FIG. 2A is formed into a smoother contour shown in FIG. 2B having a resolution which is improved to four times that of the stepped contour shown in FIG. 2A, by dot interpolation. The features of this contour portion can easily be extracted, by storing within the template matching circuit 2 collating templates which are dependent on the patterns of each of the contours.
FIG. 3 is a diagram showing collating template patterns and corresponding corrected dot outputs for some of pattern numbers. More particularly, FIG. 3 shows the collating template patterns (collating patterns) of the collating template group 6 for carrying out the dot interpolation described above in conjunction with FIGS. 2A and 2B by extracting the extracted window pattern 5 which is made up of 5 pixelsxc3x975 pixels of the input image data, and the corresponding corrected dot outputs, for some of pattern numbers 0301 through 0334. The collating templates shown in FIG. 3 are used for the dot interpolation of the image data shown in FIG. 2A and the image data which is obtained by rotating the image data shown in FIG. 2A by 180 degrees.
In the collating patterns shown FIG. 3, a symbol xe2x80x9cxe2x80xa2xe2x80x9d indicates a pixel position which is not included in the target of the pattern matching, a symbol xe2x80x9cxe2x97xafxe2x80x9d indicates a position of a black pixel, a symbol xe2x80x9c∘xe2x80x9d indicates the position of a white pixel, and a center of the collating pattern indicates a pixel which is the target of the correction.
According to the conventional smoothing process which uses the template matching, it is necessary to prepare a large number of collating patterns in order to obtain a large image quality improving effect. In addition, in order to further improve the image quality, it is necessary to extract a window pattern which is as large as possible. However, as the extracted window pattern becomes larger, the number of collating patterns which must be prepared in advance increases. As a result, an extremely large memory capacity is required in order to store the collating template group 6 in the template matching circuit 2 and the scale of the associated logic circuits becomes extremely large, thereby making it difficult to realize an inexpensive smoothing circuit.
On the other hand, the accuracy with which the features of the contour can be detected deteriorates if the number of collating patterns is limited, thereby making it difficult to obtain a large image quality improving effect when the number of collating patterns is limited.
Accordingly, it is a general object of the present invention to provide a novel and useful smoothing method, smoothing circuit, image forming apparatus and display unit, in which the problems described above are eliminated.
Another and more specific object of the present invention is to provide a smoothing method, a smoothing circuit, an image forming apparatus and a display unit which can extract features of a contour with a high accuracy by using a small number of collating patterns, and can obtain a large image quality improving effect using a relatively simple and inexpensive structure.
Still another object of the present invention is to provide a smoothing method comprising the steps of (a) selectively outputting one of an extracted window pattern which is obtained by extracting a region having a predetermined size with a target pixel formed by each pixel of an input image data, and an inverted window pattern which is obtained by inverting a polarity of each pixel of the extracted window pattern; (b) collating an output window pattern which is output by the step (a) with a plurality of collating templates, and outputting corrected dot data corresponding to one of the collating templates matching the output window pattern; and (c) selectively outputting one of the corrected dot data output by the step (b), and an inverted corrected dot data which is obtained by inverting a polarity of each dot of the corrected dot data. According to the smoothing method of the present invention, it is possible to extract features of a contour with a high accuracy by using a small number of collating patterns, and can obtain a large image quality improving effect using a relatively simple and inexpensive structure.
A further object of the present invention is to provide a smoothing circuit comprising a window pattern conversion circuit which receives an extracted window pattern which is obtained by extracting a region having a predetermined size with a target pixel formed by each pixel of an input image data, and selectively outputs one of the extracted window pattern and an inverted window pattern which is obtained by inverting a polarity of each pixel of the extracted window pattern; a template matching circuit which collates an output window pattern which is output by the window pattern conversion circuit with a plurality of collating templates, and outputs corrected dot data corresponding to one of the collating templates matching the output window pattern; and a dot data conversion circuit which selectively outputs one of the corrected dot data output by the template matching circuit, and an inverted corrected dot data which is obtained by inverting a polarity of each dot of the corrected dot data. According to the smoothing circuit of the present invention, it is possible to extract features of a contour with a high accuracy by using a small number of collating patterns, and can obtain a large image quality improving effect using a relatively simple and inexpensive structure.
Another object of the present invention is to provide an image forming apparatus comprising a smoothing circuit; and an image forming section which forms an image on a recording medium based on an output of the smoothing circuit, wherein the smoothing circuit comprises a window pattern conversion circuit which receives an extracted window pattern which is obtained by extracting a region having a predetermined size with a target pixel formed by each pixel of an input image data, and selectively outputs one of the extracted window pattern and an inverted window pattern which is obtained by inverting a polarity of each pixel of the extracted window pattern; a template matching circuit which collates an output window pattern which is output by the window pattern conversion circuit with a plurality of collating templates, and outputs corrected dot data corresponding to one of the collating templates matching the output window pattern; and a dot data conversion circuit which selectively outputs one of the corrected dot data output by the template matching circuit, and an inverted corrected dot data which is obtained by inverting a polarity of each dot of the corrected dot data. According to the image forming apparatus of the present invention, it is possible to extract features of a contour with a high accuracy by using a small number of collating patterns, and can obtain a large image quality improving effect using a relatively simple and inexpensive structure.
Still another object of the present invention is to provide a display unit comprising a smoothing circuit; and a display section which displays an image based on an output of the smoothing circuit, wherein the smoothing circuit comprises a window pattern conversion circuit which receives an extracted window pattern which is obtained by extracting a region having a predetermined size with a target pixel formed by each pixel of an input image data, and selectively outputs one of the extracted window pattern and an inverted window pattern which is obtained by inverting a polarity of each pixel of the extracted window pattern; a template matching circuit which collates an output window pattern which is output by the window pattern conversion circuit with a plurality of collating templates, and outputs corrected dot data corresponding to one of the collating templates matching the output window pattern; and a dot data conversion circuit which selectively outputs one of the corrected dot data output by the template matching circuit, and an inverted corrected dot data which is obtained by inverting a polarity of each dot of the corrected dot data. According to the display unit of the present invention, it is possible to extract features of a contour with a high accuracy by using a small number of collating patterns, and can obtain a large image quality improving effect using a relatively simple and inexpensive structure.
Therefore, the present invention can carry out a smoothing process (dot correction) equivalent to that of a conventional smoothing circuit by using only one-half the number of collating templates required by the conventional smoothing circuit. In other words, it is possible to extract the features of the contour with a high accuracy and to obtain a high-quality image, using a small number of collating templates. In addition, because the number of collating templates required is reduced compared to that of the conventional smoothing circuit, the present invention can simplify the structure and reduce the cost of the smoothing circuit. Moreover, it is possible to add different collating templates for the purposes of further improving the image quality using approximately the same number of collating templates as the conventional smoothing circuit.
Furthermore, the present invention can realize a smoothing process (dot correction) which is equivalent to that of the conventional smoothing circuit, using one-half the number of collating templates required by the conventional smoothing circuit, and by carrying out only one template collating cycle per pixel of the input image data. For this reason, the present invention can realize a high-speed smoothing process using a small number of collating templates to realize a high-quality image.
Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.